Defect
engineering can modify the physical and chemical properties
of two-dimensional (2D) materials to advance their effectiveness for
applications. Here, we have designed three kinds of single carbon
vacancies (VC‑I of BC2N-II as well as
VC‑III and VC‑IV of BC2N-III) to systematically investigate their Li adsorption and diffusion
performance based on DFT calculations. The electronic structure analysis
shows that the existence of the defects plays a crucial role to tune
the electronic properties and the performance of BC2N-II
and BC2N-III monolayers toward the potential application
as anodes of lithium-ion batteries (LIBs). Significantly, compared
to the pristine BC2N-II and BC2N-III monolayers
that can hardly adsorb Li atoms, defective BC2N monolayers
greatly enhance the Li adsorption energy. In addition, the theoretical
capacities of defective BC2N monolayers, especially for
VC‑I of BC2N-II (2256 mAh/g), are extremely
high, but the energy barriers of Li transfer in the vicinity of the
defective BC2N are relatively large, whereas for escaping
defective sites, these levels are comparatively small. Considering
the diffusion behavior of Li in the actual process of Li insertion
in the anode of the LIBs, we further explored the adsorption and diffusion
performance of Li on the modified VC‑I monolayer
with one Li atom occupying the most stable position (site H) of the
defect. Remarkably, the Li can shuttle between the stable sites around
the defects with energy barriers as low as 0.45 eV. The calculated
voltages for all systems are all within the desired ranges of reported
anode materials for LIBs. Our findings provide a theoretical guideline
to design reasonable anode materials with defect for LIBs.